1. Field of the Invention
This invention relates to improvements in a continuous process for producing rubber modified high-impact resins. More particularly, it relates to an improved process for producing rubber modified high-impact resins wherein a raw material solution comprising a mixture of an aromatic vinyl monomer and a vinyl cyanide monomer and a rubber component dissolved therein is continuously subjected to bulk or solution polymerization to obtain a rubber modified high-impact resin exhibiting excellent chemical resistance, thermal resistance and rigidity and having a good surface gloss.
2. Description of the Prior Art
High-impact polystyrenes (hereinafter referred to as "HI-PS resins") are resins obtained by polymerizing styrene in the presence of a rubber component to improve the impact resistance of the polystyrene and are being used in a wide range of applications. Although HI-PS resins are sometimes produced by batch polymerization processes (such as bulk--suspension polymerization processes), there is a recent tendency toward the increasing use of continuous bulk polymerization processes. On the other hand, acrylonitrile-butadiene-styrene copolymeric resins (hereinafter referred as "ABS resins") obtained by polymerizing styrene and acrylonitrile in the presence of a rubber component have found many uses by reason of their excellent impact resistance, chemical resistance, thermal resistance and rigidity as well as their good surface gloss. Generally, ABS resins are being produced by the so-called emulsion polymerization process in which styrene and acrylonitrile are added to a latex containing a rubber component and the resulting mixture is subjected to polymerization. However, a number of problems are encountered in carrying out this emulsion polymerization process. Specifically, large-scale polymerization equipment is required because the latex must be used in an amount equal to several times that of the desired polymer; the process control is complicated because a number of incidental steps such as emulsification, coagulation, drying and other steps are involved; and the resulting polymer may be unavoidably contaminated with impurities because such additives as emulsifiers, coagulants and the like are used. Accordingly, Japanese Patent Publications No. 35354/'74 and No. 35355/'74 have proposed improved emulsion polymerization processes for producing ABS resins in which the rubber component present in the latex is first extracted with styrene and acrylonitrile and the resulting reaction mixture is then subjected to continuous bulk polymerization. Although these improved processes are simpler than the conventional emulsion polymerization process, they still involved a complicated extraction step.
In addition to the above, continuous bulk or solution polymerization processes for producing ABS resins have also been proposed. They are disclosed, for example, in B.P. No. 1,121,885, D.E. No. 2,152,945, U.S. Pat. No. 4,198,383 and the like. It is mentioned therein that these processes have the advantages of simplifying the polymerization and after-treatment steps and decreasing the production of waste materials tending to induce environmental pollution. However, these processes are disadvantageous in that the resulting resins do not always exhibit excellent properties, their surface gloss especially characteristic of ABS resins may be impaired, and/or special equipment is needed.